The difference is typically only the policy of the company you're dealing with. The term pre-approval is considered by many to carry more legal baggage than the term pre-qualification, so its use is restricted in some quarters. Either way, it's based merely on your credit report and some unverified Q&A.
A pre-approval or prequal is generally issued by your loan officer or mortgage broker early on, to lend credibility to an offer. It does *not* go to an underwriter and is definitely not indicative of your file being processed, submitted, and conditionaly approved in underwriting. That would be an approval, not a pre-approval. - Tue May 12 2009, 09:20